initial support for tabbed R Markdown template options
organize and order options
add support for nullable numeric options
add support for R Markdown nullable string options
improve spacing of options in template options dialog
Merge pull request #98 from rstudio/feature/output-options

Simplify R Markdown creation experience and organize options
elaborate descriptions for output formats
Remove icons from New R Markdown dialog
Remove settings icon/explanation from bottom of New R Markdown dialog
Increase width of New R Markdown dialog
Use lighter color for Rmd format explanations rather than names
use common code for image menu items
support list elements as values in YAML tree reordering
Merge pull request #99 from rstudio/feature/rmd-dialog-asthetics

Simplify and improve aesthetics for New R Markdown dialog
show Word icon for Word documents
vertically align icons with text in constructed menus
style GWT tab panel in R Markdown format options
emit knitr errors encountered during R Markdown render to client
don't automatically download rendered Word docs in server mode
remove pandoc command line arguments option in R Markdown dialog